Castor



FIG. 1 is a frontal perspective view of my ornamental design;

FIG. 2 is a rear perspective view of the ornamental design of FIG. 1;

FIG. 3 is a side elevation view of the ornamental design of FIG. 1;

FIG. 4 is a top view of the ornamental design of FIG. 1;

FIG. 5 is a front plan view of the ornamental design of FIG. 1;

FIG. 6 is a rear plan view of the ornamental design of FIG. 1; and,

FIG. 7 is a bottom view of the ornamental design of FIG. 1.

The broken lines in the drawing depict environmental subject matter only and form no part of the claimed design. 

The ornamental design for a castor, as shown and described. 